超電導接合を用いた永久電流1.3 GHz (30.5 T) NMRに向けて−永久電流400 MHz (9.39 T) LTS/REBCO NMR 用REBCO内層コイルの単体試験特性− (Towards a persistent current 1.3 GHz NMR using superconducting joints - Test results of a REBCO inner coil for a persistent 400 MHz (9.39 T) LTS/REBCO NMR -)